1. Field of the Invention
The present invention relates to variants of an alpha amylase, polynucleotides encoding the variants, methods of producing the variants, and methods of using the variants.
2. Description of the Related Art
The present invention provides variants of a parent alpha amylase with improved properties compared to its parent. Alpha-amylases (1,4-α-D-glucan glucanohydrolase, EC 3.2.1.1) constitute a group of enzymes which catalyze hydrolysis of starch and other linear and branched 1,4-glucosidic oligo- and polysaccharides.
There is a very extensive body of patent and scientific literature relating to this industrially very important class of enzymes. A number of alpha-amylases referred to as “Termamyl®-like alpha-amylases” and variants thereof are known from, e.g., WO 90/11352, WO 95/10603, WO 95/26397, WO 96/23873 and WO 96/23874. Termamyl®-like alpha-amylases are very thermostable and therefore suitable for processes carried out at high temperatures such as starch liquefaction in dextrose production processes.
Another group of alpha-amylases are referred to as “Fungamyl™-like alpha-amylases”, which are alpha-amylases related or homologous to the alpha-amylase derived from Aspergillus oryzae. The Fungamyl-like alpha-amylases have a relatively low thermostability e.g. the commercial product sold under the tradename FUNGAMYL™ by Novozymes A/S, Denmark, has an optimum around 55° C., and is not suitable for processes carried out at high temperatures. Fungamyl™-like alpha-amylases are today used for making syrups for, e.g., the brewing industry.
An alpha-amylase with increased thermostability, preferably at an acidic pH, has previously been successfully isolated. WO 2004/055178 discloses a gene from Rhizomucor pusillus encoding an alpha-amylase denoted AM782. Characterization of this amylase has shown it to be a highly thermoacidophilic alpha-amylase which has a highly interesting activity as demonstrated by the sugar profile from maltodextrin hydrolysis by amylase AM782. The amylase AM782 can work at a very high temperature, at least up to 70° C. However, this alpha amylase has poor storage stability if stored without cooling. It is an object of the present invention to provide storage stable variants of AM782 as SEQ ID NO: 3 (mature polypeptide), which have retained good raw starch hydrolysis activity.